Camshaft phasers for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. In a typical prior art vane-type cam phaser, a controllably variable locking pin is slidingly disposed in a bore in a rotor vane to permit rotational locking of the rotor to the stator under certain conditions of operation of the phaser and engine.
A known locking pin mechanism includes a return spring to urge an end of the pin slidably mounted in a rotor into a hardened seat disposed in the stator of the phaser, thus locking the rotor with respect to the stator. In operation, the pin is forced from the seat to unlock the rotor from the stator by pressurized oil supplied from a control valve, overcoming the seating spring, in response to a programmed engine control module (ECM). The oil may be applied to the end of the pin and/or to the underside of a pin shoulder via passages formed in the rotor and/or the pulley/sprocket.
A prior art vane-type phaser generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve (OCV), in accordance with an engine control module, to either the advance or retard chambers, to change the angular position of the rotor relative to the stator, as required to meet current or anticipated engine operating conditions. As used herein, the advance chambers are referred to as C1 and the retard chambers are referred to as C2. Thus, the corresponding actuating oil pressures are referred to as C1 oil and C2 oil.
In a typical prior art phaser, engagement or disengagement of the locking pin is tied to C1 or C2 oil pressure. That is, the pin is locked or unlocked, via appropriate porting, by the same oil supply that drives either the advance or retard of the phaser.
A problem in such prior art phasers is that the pressure requirements and timing of advance and retard can be quite different than those for pin movement under some engine operating conditions. It is well known in the art, for example, that a locking pin may become stuck in lock mode when chamber pressure increases faster than the pin can respond, causing the rotor to try to rotate before the locking pin is fully retracted, thereby binding the pin in the locking seat. Further, oil pressures may be too low to reliably actuate the locking pin, even when the rotor is properly actuated.
A problem in some prior art phasers is that re-engagement of the pin end with the stator seat can be uncertain. If the pin and seat are both cylindrical, near-perfect registration is required, plus a finite period of registration, for the pin to enter the seat. If the pin fails to fully engage the seat, the pin can be forced out of the seat during engine operation when locking engagement is required, which is highly undesirable.
To overcome this problem, it is known in the art to bevel, chamfer, or taper the pin to assist in its entry into the seat. See, for example, U.S. Pat. No. 5,865,151. However, such a non-cylindrical pin can be forced from the seat by pressure fluctuations in the phaser advance and retard chambers caused by torque reversals imposed on the camshaft during valve opening and closing events. To overcome this problem, it is known to axially offset the pin axis from the seat axis. In prior art phasers, the locking position of the rotor is typically in full valve-retard mode, wherein at least one rotor vane is in mechanical contact with a lobe of the stator. The offset pin acts to wedge the rotor firmly against the stator such that the rotor position cannot fluctuate under torque reversals imposed on the camshaft. This offset pin design is known in the art as a “negative gap”.
In prior art intake valve phasers, the rotational range of phaser authority is typically about 50 degrees; that is, from a piston top-dead-center (TDC) position, the valve timing may be advanced to a maximum of about −40 degrees and retarded to a maximum of about +10 degrees. Because the rotor is stopped by the stator, further advance or retard, should it be desired under special circumstances, is not possible in a prior art phaser. Further, a prior art phaser is not adapted for rotor-locking an intermediate authority position, as would be required.
Surprisingly, in certain situations such as, for example, for engines having intake valve and exhaust valve camshaft phasers (dual independent cam phasing, DICP), it has been found that additional intake valve retard authority, amounting to about an additional 20 crankshaft degrees, can be highly beneficial in improving fuel economy under conditions of partial engine load. Prior art phasers are not capable of this beneficial extended authority.
What is needed in the art is an improved vane-type camshaft phaser having additional range of rotational authority in the retard direction, means for locking of the rotor to the stator at an intermediate locking position (ILP) comparable to the full-retard position of a prior art phaser, and a reliable oil supply (C3) separate from either C1 or C2.
It is a principal object of the present invention to improve fuel economy in an internal combustion engine.
It is a further object of the present invention to improve the reliability of locking pin action in a vane-type camshaft phaser.